ULTRASTRUCTURE OF NICOTIANA ALATA POLLEN, ITS GERMINATION AND EARLY TUBE FORMATION

Both internal anatomy and external morphology of the mature pollen grain of Nicotiana alata have been studied, together with pollen activation and tube emergence and its cytological zonation. A peculiar feature of mature pollen is the occurrence in the vegetative cell cytoplasm of a large quantity of stacked cisterns of rough endoplasmic reticulum, which then dissociate during pollen activation. Pollen tube emergence generally occurs 2 hr 30 min after hydration, while cytological zonation is complete 4 hr 30 min after hydration when the first callosic plug is formed.